1. Field of the Invention
The present invention relates to an image reader used in a facsimile telegraph, an image scanner, etc. More particularly, the present invention relates to an image reader made compact by using a roof mirror lens array.
2. Description of the Related Art
Recently, a demand for a more compact image reader having higher performance has been increased as a facsimile telegraph, an image scanner, etc. are personally used.
FIG. 1 is a cross-sectional view showing a main portion of a general image reader for satisfying such a demand. For example, this image reader is shown in Japanese Patent Application Laying Open (KOKAI) No. 4-245765.
In FIG. 1, image information of an original 2 arranged on a glass stage 1 is read by a reading unit 3 moved in a cross scanning direction along a lower face of the glass stage 1.
The reading unit 3 has a light source 5, a roof mirror-lens array 7, an optical path separating mirror 8 and a one-dimensional image sensor 9 within a case 4. The light source 5 illuminates the original 2 through the glass stage 1. The roof mirror lens array 7 converges light reflected on the original 2 and this converged light 8 is reflected on the roof mirror lens array 7. In the following description, the roof mirror lens array 7 is called RMLA. The optical path separating mirror 8 perpendicularly refracts the reflected light from the roof mirror lens array 7. The one-dimensional image sensor 9 separates the light received from the optical path separating mirror 8 into pixels and photoelectrically converts this light. The one-dimensional image sensor 9 outputs a series of electric signals corresponding to image information on one line of the original 2 in a main scanning direction. A shield plate 10 is arranged to prevent stray light from the light source 5. Reference numerals 11 and 12 respectively designate a substrate of the one-dimensional image sensor 9 and a base for attaching the substrate 11 thereto.
The roof mirror lens array (RMLA) 7 is constructed by a lens array 13, an intermediate member 14 and a roof mirror array 15. In the following description, the lens array 1S and the roof mirror array 15 are respectively called LA and RMA. External appearances of the lens array 13 and the roof mirror array 15 are shown in FIG. 2.
In FIG. 3, the lens array (LA) 13 has an elongated frame body 18 and many convex lenses 17 arranged in a line inside the frame body 18 and equally spaced from each other. The frame body 18 and the convex lenses 17 are integrally formed by pressing and molding a transparent material such as plastic, etc. The roof mirror array (RMA) 15 has many roof type reflecting faces 18 arranged at the same interval as the convex lenses 17. For example, each of the roof type reflecting faces 18 is finished as a mirror face by a finishing technique such as evaporation, etc.
In accordance with the roof mirror lens array 17 constructed above, the reflected light from the original 2 passes through the lens array 13 and is reflected on the roof mirror array 15. An optical axis of this reflected light is bent by the optical path separating mirror. Thereafter, for example, an alphabet image A is focused and formed on a light receiving face of the one-dimensional image sensor 9 in FIG. 2. Accordingly, an entire height of the image reader can be reduced in accordance with a distance L from the original 2 to the roof mirror array 15 so that the image reader can be made compact.
However, the general image reader using such a roof mirror lens array (RMLA) takes no sufficient light shielding action between many convex lenses constituting the lens array (LA). Therefore, flare tends to be caused by light passing around between adjacent convex lenses. Accordingly, for example, an output level of a black portion of the image rises so that this black portion seems gray. Otherwise, thin lines of the image are interrupted by deterioration of resolution characteristics generally evaluated by the concept of a modulation transfer function (MTF). Accordingly, there are technical subjects to be improved with respect to the quality of a read image.
Each of FIGS. 4a and 4b is a view for explaining generation of flare and shows a conceptual view provided when a black portion shown by a black square mark is scanned along a scanning line 20. In the case of flare generation shown in FIG. 4a, an output voltage level of the black portion is slightly higher than a minimum voltage level corresponding to a dark output level of the one-dimensional line sensor. This slight higher portion of the output voltage as a rising level portion corresponds to a passing-around portion of light from white portions before and after the black portion. When there is no passing-around light, no flare is generated as shown in FIG. 4b. In FIG. 4a, an error in black level is clearly recognized in comparison with FIG. 4b.